1. Field of the Invention
The present invention relates to an electric shaver and more particularly to an electric rotary shaver.
2. Prior Art
Generally, in electric shavers, particularly in electric rotary shavers, inner cutters are rotated on the under surface of outer cutters; and the hair is cut by the shearing force generated between these two cutters. In some shavers, only one single shaving unit that consists of an inner cutter and an outer cutter is installed in the shaver head of the shaver; and there are also shavers in which two shaving units or three shaving units are installed in the shaver head, each being called a twin-headed shaver and a triple-headed shaver, respectively. In the twin-headed shaver, the shaving units are arranged side by side; and in the three-headed shavers, the shaving units are generally arranged in an inverse equilateral triangle shape so as to obtain the most efficient shaving results.
In any of these shavers currently marketed, only the inner cutters are rotated by a motor installed inside the shaver casing so that the shearing force is obtained between the rotating inner cutter and the non-rotating outer cutter which are designed to be inwardly depressible during shaving.
Since the outer cutter which ordinarily has radial slits for introducing facial hair is not rotated as described above, the hair does not enter into the slits easily, resulting in that shaving is occasionally not performed efficiently. So as to execute a smooth and efficient shave, it is common to move the shaving head (and therefore the outer cutters) circularly on, for example, the face, which sometimes causes muscle fatigue in the arm that holds the shaver; and therefore, such a prior art shaver has a problem with the shaving effect and with the use thereof.